Amrit means nectar, and manthan means churning:
By drinking nectar one becomes immortal. So say Puranas.
Here is the story of Amrita Manthan.
Rishi Kashyapa had two wives. They were called Diti and
The children of Diti were the Asuras or demons, and those
of Aditi were the Devas or angels. The demons and angels were thus cousins.
The cousins always quarreled.
Once, Rishi Durvasa cursed the Devas for showing him
Because of the curse; the Devas were defeated by the demons